The present invention relates generally to laser printing.
FIG. 1 depicts a cross-section view of a typical laser printer 100. During operation of the printer, a substantially uniform charge is placed on the surface of drum 101 by charge roller 102, or alternatively, by a corona wire. Laser beam 103, controlled by a steering mechanism represented by mirror 112, selectively illuminates areas of drum 101. This illumination at least partially discharges those areas of drum 101, for example by photoconduction to a conductive substrate in the drum. The selective discharging of areas on drum 101 forms a latent image on drum 101.
FIG. 2 shows a magnified view of the resupply roller region of FIG. 1. Particles of toner 104 carrying an electric charge are taken from a toner supply container 105 by resupply roller 106 and deposited on the surface of developer sleeve 107. Developer sleeve 107 is depicted as a cylinder in this example printer, but other printers may use other toner receiving surfaces. For example, the toner may be received onto a belt. A leveling blade 113 may assist with the distribution of toner on developer sleeve 107.
Developer sleeve 107 carries a voltage bias such that when the toner-coated developer sleeve 107 makes rolling contact with drum 101, the charged toner particles are attracted to the discharged areas on drum 101, and repelled from the still-charged areas on drum 101. In this way, toner is collected on selected portions of the surface of drum 101, forming an image in toner 110 on the drum surface.
As drum 101 rotates further, the toner image 110 is brought into rolling contact with paper 108 between drum 101 and transfer roller 109. Transfer roller 109 carries a voltage bias such that the charged toner particles are strongly attracted to it, and thus pulled from the surface of drum 101 onto the surface of paper 108. The toner image 110 is thus transferred to the surface of paper 108.
The paper, carrying the toner image, then passes through a fuser mechanism 111. The fuser mechanism 111 may consist of one or more heated rollers that briefly melt the toner particles, fusing them to paper 108. After passing through the fuser mechanism, paper 108 carries a substantially permanent image.
It is the object of resupply roller 106 to coat developer sleeve 107 with a layer of toner particles. The resupply roller 106 may have longitudinal ribs for assisting in the mechanical transfer of toner 104 to developer sleeve 107.
While the ribs may greatly facilitate the movement of toner 104 to developer sleeve 107, they may also affect the quality of the image eventually produced on paper 108. The mechanical interaction of the ribs with developer sleeve 107 may excite minute vibrations in the printer mechanism, or the toner may not be placed on developer sleeve 107 with perfect uniformity. These effects may cause banding in the final printed image, especially when the image being printed is a photograph or other graphical element.
There is a need for an improvement to the resupply roller so that image artifacts are reduced.
A toner resupply roller in a laser printer has ribs that are not parallel to the rotational axis of the roller. The ribs form a tilted, helical, herringbone, or other pattern on the roller.